Gorillas, monkeys, lemurs and other primates are in danger of becoming extinct.

Zistboom: Gorillas, monkeys, lemurs and other primates are in danger of becoming extinct, and scientists say it's our fault that our closest living relatives are in trouble, a new international study warns.

About 60 percent of the more than 500 primate species are "now threatened with extinction" and 3 out of 4 primate species have shrinking populations, according to a study published in Wednesday's journal Science Advances.

While scientists had tracked dwindling numbers of individuals and groups of primates in forests around the world, this is the first big-picture look. The result was "a bigger wake-up call" than previously thought, said researcher Paul Garber of the University of Illinois.

"The outlook is not very good," said Garber, who recently returned from the jungles of Brazil studying marmosets.

The decline has been blamed on human activities including hunting, mining and oil drilling. Logging, ranching and farming have also destroyed precious habitat in Africa, Asia and South America.

Primates, which include apes, monkeys and humans, have forward-facing eyes and grasping ability that set them apart from other mammals. Scientists study them to learn about human behavior and evolution.

Much of the problems faced by primates are recent. For example, the Grauer's gorilla dropped from a population of 17,000 in 1995 to just about 3,800 now, mostly from bushmeat hunting and mineral mining, the study found.

There are only about 14,000 Sumatran orangutans left in the world. The Hainan gibbon in China is down to just 25 individuals, while 22 out of the 26 primate species in China are endangered, Garber said.

About 94 percent of the lemur species in the world are endangered, especially in Madagascar, which is one of hardest-hit places for primate population loss.

"We need to look at (population losses) almost as signals. They're telling us something about our future," Garber said. "This is a critical world problem."

While there's hope that some species can be protected, many will disappear in the coming decades, said co-author Eduardo Fernandez-Duque of Yale University.

Emory University primate expert Frans de Waal called the work "very detailed and timely and unfortunately correct."

"Primate populations are clearly moving in the wrong direction," said de Waal, who wasn't part of the study.